Despite significant advances in imaging speed over the past decade, many diagnostic applications of magnetic resonance imaging (MRI) are still limited by rapid physiologic motion. An order of magnitude improvement in imaging speed would remedy many of the existing technical limitations associated with motion; however, certain basic constraints of conventional MR imaging techniques have made this goal difficult to attain. We have recently developed and implemented an MR imaging technique called SiMultaneous Acquisition of Spatial Harmonics (SMASH), which can relax these constraints by allowing for a significant fraction of signal data points to be acquired in parallel, rather than in the traditional sequential order. Cardiac MRI is one area which stands to benefit substantially from the improvements in imaging efficiency afforded by SMASH. The application of MRI to the diagnosis and assessment of cardiac disease has been an area of intensive study in recent years, but its practical clinical implementation has generally been hindered by competing constraints of spatial and temporal resolution. In preliminary in vivo studies using SMASH, the temporal resolution of cardiac scans has been increased as much as threefold without any sacrifice in spatial resolution, and spatial resolution has been doubled or tripled at no cost in temporal resolution. Recent SMASH imaging studies in phantoms, furthermore, have demonstrated that eightfold improvements in spatial and/or temporal resolution are feasible using appropriate RF coil array technology. The ability to achieve reliable time saving factors as high as eight in cardiac MRI will require several theoretical and technical advances. The primary goal of the proposed research is to extend the basic capabilities of SMASH imaging so as to achieve an eighfold improvement in the spatial and/or temporal resolution of cardiac MR images. A stepwise approach will be followed, with the following specific aims: 1)To increase the flexibility of SMASH techniques for cardiac imaging, starting at the current level of two- to threefold speed improvements. 2)To achieve a factor of four to six improvements through the further design and implementation of SMASH hardware and software. 3) To extend these improvements to a factor of eight or more, and to apply these improvements to clinical cardiac imaging.